Query optimization depends in large part on efficient and accurate cardinality estimates of intermediate results and the plan for the order of a sequence or set of operators representative of a query. In some aspects, the order of the operators to implement the query may be determined with relative ease, particularly as compared to the process of accurately determining a cardinality estimate.
Various methods have been previously proposed for determining cardinality estimates. However, a number of the previous proposals may result in unbounded estimation errors. Also, since the building of a histogram typically involves the accessing of data via a data scan the manner in which the data is stored may impact the efficiency of the histogram construction.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.